Print hammer unit for high speed printers

ABSTRACT

PRINTING APPARATUS FOR A HIGH SPEED PRINTER HAVING AN ELONGATED PRINT HAMMER WITH AN UPSTANDING ARMATURE PORTION AT THE END REMOTE FROM THE PRINT LINE AND A PAIR OF PARALLEL FLAT SPRINGS SUPPORTING THE PRINT HAMMER. AN ELECTROMAGNET HAVING A HOLD WINDING FOR PRODUCING MAGNETIC FLUX TO HOLD THE PRINT HAMMER IN A RETRACTED POSITION AND MEANS FOR REDUCING THE MAGNETIC FLUX BELOW THE HOLDING VALUE TO PERMIT THE SUPPORT SPRINGS TO ACTUATE THE HAMMER TO A PRINTING POSITION.

Spt. 21, 1,71 sl ARNOLD ETAL Re. 27,115

PRINT HAMMER UNIT FOR HIGH SPEED PRINTERS Original Filed July 19. 1965 8Sheets-Sheet 1 INVENTORS SIEGHARD ARNOLD GEROLD BUHRMANN J URGEN H ASISEBERHARD SPIETH mgl/1M Y ITTUHII EY Sept. 2l, 1971 s, ARNOLD ETAL PRINTHAMMER UNIT Fon HIGH SPEED PRINTERS Original Filed July 19, 1965 Sept.21, 1971'V 5 ARNQLD ETAL Re. 27A

PRINT HAMMER UNIT FOR HIGH SPEED FRINTERS Original Filed July 19. 1965 8Sheets-Sheet .5

Sept. 21, 1971 s ARNOLD Em RQ. 21,115

PRINT HAMMER UNIT FOR HIGH SPEED PRINTERS Original Filed July 19. 1965 8Sheets-Sheet 4.

Sept. 21,'1971 s, ARNOLD EI'AL PilNT HAMMER UNIT FOR HIGH SPEED PRINTERS8 Sheets-Sheet 5 Original Filed July 19. 1965 FIG. 8o

FIG.8

FIG.7

Sq. 21, 1971 ARNOLD ETAL Re. 27,115

PRINT HAMMER UNIT FOR HIGH SPEED PRINTERS Original Filed July 19. 1965 8Sheets-Sheet 6 S. ARNOLD ETAI- APRINT Hum UNIT F011 HIGH SPEED rnINTnRssept. 21, 1911 8 YSheets-.Sheet 7 or1g1na1 Fued'auly 19. 1965 FIG. 1o

sept. 21, 1971 SARNQLD Em Re. 21,115

PRINT HAMMER UNIT FOR HIGH SPEED PRINTERS Original Filed July 19. 1965 8Sheets-Sheet B FIG.v 12u ,M 111 ly a (ma 11111111511 1110111 11115 vs.11u01 011111 110011 oFF 111 x 11010111 I ,l l l A 245 0,90 1,12 1,2111,44 '0 's 1,112Y 2,011 2,24 2,40

Fm- 11111111E11 1110111 11115 115.11011110Ev Y Y FIQ.` 12e11111111112111110111 v 1111i/ //////A 101. 1 '15011 (vous) 100% vomcEFOR HoLD A110 BUCK 0FF111|1101110 United States Patent O 27,175 PRINTHAMMER UNIT FOR HIGH SPEED PRINTERS Sieghard Arnold, Hildrizhausen,Gerold Buhrmann, Stuttgart, Jurgen Haasis, Boblingen, Horst Heinrich,Berlin, Manfred Nitschke, Stuttgart-Rohr, Gunter Schacht, Boblingen, andEberhard Spieth, Holzgerlingen, Germany, assignors to InternationalBusiness Machines Corporation, Armonk, N Y.

Original No. 3,359,921, dated Dec. 26, 1967, Ser. No. 473,093, July 19,1965. Application for reissue Apr. 29, 1968, Ser. No. 728,093

Claims priority, application Germany, July 25, 1964, J 26,273 Int. Cl.1341i 9/00; B23p 19/00 U.S. Cl. 101-93 20 Claims Matter enclosed inheavy brackets appears in the original patent but forms no part of thisreissue specification; matter printed n italics indicates the additionsmade by reissue.

ABSTRACT F THE DISCLSURE Printing apparatus for a high speed printerhaving an elongated print hammer with an upstanding armature p0rtion atthe end remote from the print line and a pair of parallel flat springssupporting the print hammer. An electromagnet having a hold winding forproducing magnetic ilux to hold the print hammer in a retracted positionand means for reducing the magnetic ux below the holding value to permitthe support springs to actuate the hammer to a printing position.

This invention relates to a print hammer unit, and in particular to aprint hammer unit for a high speed printer which is used as an outputdevice for an electronic data processing machine.

Generally, modern high speed printers of this type work in such a mannerthat a type carrier is provided which c011- tains several sets of allcharacters to be printed, and which carries out a periodic movement sothat each printable character is offered to each print position of aprint line. A rotating type drum, a type chain, moving in the print linedirection or a type bar moving back and forth periodically in the printline direction can be used a type carrier. At each print position of aprint line a print hammer is provided which is released at a suitablemoment, i.e., when the type to be printed is in the corresponding printposition. For the control of the print hammer impact an electronicrepresentation is formed of the print type which is in an individualprint positions each time, with reference to a certain position of thetype carrier. In a socalled scan, in passing from print position toprint'position, this electronic representation is compared with the textof a print line which is also stored electronically in a data processingmachine. If the two coincide for any print position, the print hammercorresponding to this print position is released.

A particularly diticult problem connected with such high speed printersoccurs in the print hammer mechanism. On the one hand, it is verydifficult to make the individual print hammers and their drives of suchan extreme flatness that they do not take up more space than the widthof a print character, and to arrange all the print hammers closelypacked in a row of approximately 13() print positions forming the printline, and to also provide for adjustment thereof. On the other hand, theprint hammers should have a considerable but clearly defined amount ofkinetic energy in order to obtain a uniform print on several copies, andthe hammer motion, with the hammer flight time of some millisecondsduration, has to be exactly reproducible. As in general such printersfollow the principle Re. 27,175 Reissued Sept. 21, 1971 lCC of one-the-yimpact, that is, as the type carrier 'is not stopped by the hammerimpact, the contact of the print hammer with the type tiying by must beof very short duration.

A well known print hammer mechanism for such high speed printers worksin sucha manner that the armature and electromagnet accelerate the printhammer. As the magnet only res the print hammer, which then moves on infree flight, a great number of factors have to be taken intoconsideration with regard to the hammer motion, and an exactlyreproducible hammer motion can be obtained only with great diiculty.

In another well known print hammer mechanism rotational kinetic energyis transferred through a cam or through a pushing process onto the printhammer. In that application the electromagnet only effects the releaseof the print hammer at a predetermined moment, but as the print hammerenergy is taken from a continuously rotating drive, it is possible toobtain a greater exactness in the hammer motion. Such a mechanism,however, presenta considerable construction diiculties, in particular onaccount of the high mechanical stress on the parts partici pating in thepush process at increased speeds. The inertia of the control elements isanother factor impeding an increase in speed with this type ofmechanism.

In another print hammer mechanism known to the art, potential energystored in a spring is used for the print hammer drive. In that systemthe print hammer is shiftably arranged in a guide, and a stretchedspring is gripped by a latch. Here too, the release takes place througha control mechanism operated by an electromagnet.

ln order to avoid the disadvantages connected with the use of mechanicalcontrol parts, and to reduce the inertia in the control of the printhammer release, it is also known to hold the print hammer against theforce of a stretched spring through the use of a magnet, and tode-excite the magnet to obtain the print hammer release. In a well knownprint hammer unit of that kind the print hammer is supported suitably onan axle and is designed as a tWoarmed lever, the one lever arm of whichserves as an armature, whereas the actuating spring engages the otherlever arm. This print hammer mechanism, however, has as one of itsdisadvantages the fact that the support of the print hammer on an axlerequires an uncomfortably large width for the hammer drives. Throughthis support, friction losses are caused, which consume part of thehammer energy. Besides it is quite difficult to adjust all print hammersin such a manner that they t against the various magnets without airgaps, which is a condition absolutely necessary for obtaining anaccurately dened hammer motion. Finally, the magnet windings have to behoused in a very narrow winding space. This limits the power of theholding magnets, which in turn puts a limit on the strength of thedriving spring. Furthermore, this print hammer unit is complicated inits construction and requires a large amount of maintenance.

This invention, the aim of which is to provide a print hammer unitworking quickly and exactly, and which does not take up much space andoperates very safely, in addition to using a minimum of wearable partsrequiring maintenance, relates to a print hammer unit where potentialenergy which has been stored in a spring is used for print hammeractuation, and where the print hammer release is effected throughdeactivation of the magnet holding the tensioned print hammer.

In order to avoid the aforementioned disadvantages, the print hammerunit of the present invention is of such a design that potential energyis stored in elastic elements, preferably flat springs, which arerelatively rigid to tensile and torsional stress, and are subjected tobending only, and which at the same time provide supports for the printhammer, and are arranged in such a manner hat the print hammer motionconsists of a parallel novement.

Using this principle, a printing unit as disclosed by his invention isadvantageously constructed in such a nanner that the print hammers areformed as flat rods iaving a bent portion serving as an armature. Saidrods form components of an operational flatness which can Je replacedindividually, along with their supports which :onsist of two flatsprings arranged vertically and fixed n a foot plate.

More advantages of the print hammer unit as disclosed )y this inventionare that the tensioned print hammers issociated with the individualprint positions are held by neans of electromagnets consisting of amagnet yoke trranged at each print position and a magnet winding :ommonto all the magnet yokes, and that for the deactivation of theelectromagnets holding the tensioned irint hammers, release windings arearranged at the inlividual print positions on the magnet yokes in such ananner that the magnetic field each produces, compen- :ates orneutralizes the field of the holding magnet, or 'emoves it from thearmature, respectively.

In order to obtain a very short and well defined release ime of thearmature at the print hammer release, the :rint hammer unit as disclosedby the invention is of iuch a design that the magnetic field of theholding magnet s overcompensated for, through the magnetic field of hereleasing magnet at the point position in question. Furthermore, thepresent invention provides for the holdng winding, which is continuouslyenergized and which s common to all magnet yokes, to be connected inseries vith an inductance of a high value in order to avoid thenfluences of changes of the magnetizing force at the ndividual magnetyokes on the holding flux.

For obtaining a holding force independent of voltage Yariations it isadvantageous that the magnet yokes near heir pole faces have a crosssection which is reduced n comparison with the cross section of theremainder of he magnetic circuit, so that in that area they aremagietized to the saturation point.

An important advantage of the print hammer unit as lisclosed in thepresent invention is that the magnet yokes, )referably in pairs, aresecured by means of tensioned :lamps to bars mounted on a support. Ithas been found o be desirable to have impressed in the faces of the bar:urfaces and the inner jaws of the tensioned clamps pressng the magnetyokes against the bars, respectively, hard :rystals such as sinteredA1203 (corundum). This has the :ffect that the magnet yokes are soaligned individually igainst their print hammers that upon excitation ofthe nold magnets, and when their respective clamps have :een released bya key, they locate themselves against he corresponding magnet armaturewithout an air gap )ein-g formed. It is thus possible to adjust allmagnet rokes within the shortest time through a simple manipuationwithout the risk of twisting or overtensioning of he support holding themagnet yokes.

The print hammer unit disclosed by the invention is of iuch structurethat the magnet yoke support is equally iupported on leaf springs whichare arranged in such t manner that it can be shifted with a parallelmotion, ind then it carries out a movement of going periodically )ackand forth and being directed in a vertical direction elative to theplaten which serves for the return of the ired print hammers. Suchmovement is preferably efected by means of a cam gear.

An uncomplicated and safe method of securing and idjusting theindividual print hammer units is obtained n the printing device asdisclosed by the invention, by iecuring the print hammer units,preferably in pairs, by neans of foot plates to stationary guidingplates so that :he print hammer units can be shifted or adjustedirilividually.

In order to guarantee uniform connections at the clampng points of theleaf springs carrying the print hammers,

the leaf spring structures are designed in such a manner that thesprings carrying the print hammers are surrounded at their tops andbottoms with coatings of an elastic substance which fills cavities inthe print hammers and the foot plates in which the spring ends arewelded, said coatings being tapered towards the middle of the springs.

Another advantage of the print hammer unit as disclosed by thisinvention is that spring U-bolts are provided which slide in thedirection of the leaf springs carrying the print hammers, and whichfurthermore fit against the leaf springs at their ends and which arecombined structurally to be slidably supported in the foot plate of thecorresponding print hammer unit. These U-bolts serve for adjusting thehammer fiight time. Through a small shifting of these U-bolts themanufacturing tolerances in the thickness of the leaf springs carryingthe print` hammers can be compensated for.

Finally the print hammer unit of this invention is characterized in thatat the individual print positions elastically fixed damping material isprovided which absorbs the energy of the print hammers moving back afterthe print impact, and which by means of elastic stops, looks the printhammers until the magnet yokes, when moved to their extreme forwardpositions, have magnetically attracted their respective hammers. In anadvantageous manner the damping material is arranged on a supportextending over all of the print positions, which support is pivotallymovable for a short time to release stops in a downward direction, bymeans of an axle. This support is pivotally movable for a short time torelease the print hammers, preferably by means of a cam gear.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

In the drawings:

FIG. 1 is a partly broken away perspective drawing of a print hammerunit embodying the invention in one of its forms;

FIG. 2 is a schematic partly sectional view of the drive of a 'printhammer unit in side elevation and in the rest position;

PIG. 3 is the same view as shown in FIG. 2 but at the beginning of therestore motion of the print hammer;

FIG. 4 is the same view as shown in FIG. 2 but with the print hammersprings tensioned;

FIG. 5 is the same view as shown in FIG. 2 in an intermediate positionshortly after a print hammer impact;

FIG. 6 is an enlarged View of the holding magnets and their supportmeans;

FIG. 7 is a plan view of the holding magnets with their supportingclamps;

FIGS. 8a and 8b are top and side views respectively of the key used foradjusting the holding magnets and opening the support clamps;

FIG. 9 is an enlarged perspective view of the dampers at the moment ofbecoming effective upon the restore of the print hammers;

FIG. 10 is an enlarged side view of a print hammer and its support;

PIG. 11 is a sectional View along the line 11-111 of FIG. 1:0 showingmore clearly -the securing of the leaf springs at their clamping points;

12a is a schematic diagram of the circuits for the holding magnetstogether with the bucking windings therefor; and

FIGS. 12b and 12e show curves illustrating the hammer flight time v.bucking ampere turns and voltage, re'spectively.

In the printing unit shown in FIG. l a type bar I1 is used as a typecarrier which can be shifted longitudinally in a print line directionand which is designed in a comb-like form. The type bar 1 is secured toa tube 2 which moves in a guide 3. The type bar 1 is equipped withelastic tongues 4 to whose free and print types 5 are ixed. The Spacingof the individual tongues corresponds with the spacing of the printpositions of the print line. During printing the print types 5 are movedagainst a paper sheet 7 placed over a platen 6. Ribbon 8 is guided overthe paper sheet 7. A stop bar 10l inserted in the guide block 9, inwhich the guide 3 is formed in part, limits the forward movement of theelastic tongues `4.

At each print position a print hammer 11 is provided which at a suitablemoment, i.e., when through shifting of-tbe type bar 1, the type to beprinted is in the corresponding print position, strikes against the headof the elastic tongue 4 andthus effects the printing of thecorresponding type. The print hammers 11 are secured at the heads of twoleaf springs I12, 13 which in turn are clamped at their foot end in afoot plate 14. The hardness of the leaf springs 12, 13 is selected insuchfa manner that the springs are to be regarded as rigid with respectto pressure, tension, and torsion. They are only exposed to a bendingaction. Thus the movement of the print hammer secured to said springsprincipally consists of a parallel motion.

The print hammers, which may be considered as formed of little rodsconsisting of one piece, and are normally heldin a tensioned statethrough a holding magnet. For that purpose they are L-shaped and have a'bent projection 15 which serves as a magnetic armature (FIG. 6). Witheach armature 15 a magnet yoke 16 is associated which is H-shaped. Polefaces 17, 18 lie at the ends of the free legs 19, 20 of the yoke 16opposite the armature 15. A magnet winding 21 extends over all themagnet yokes 16 and is housed in the cavity in the legs 19, 2|]I andcontinuously carries current during operation, so that the holdingmagnets for the individual print hammers are continuously excited. Legs19, 20 of the magnet yokes 16 have ledges 22, 23 near the pole faces atwhich the cross section of the yokes is reduced. It thereby results thatthe magnet yoke 16 within the area of their pole faces 17, 18 aremagnetized to the saturation point, and thus the holding force of theholding magnets is independent of voltage variations. In addition, theholding winding -21 is connected in series with an inductance device Lof a relatively high value (FIG. 12a) in order to avoid the effects ofvariations in the magnetizing force of the holding circuit during thefiring of the print hammers.

For the conrtollable release of the tensioned print hammers held by thehold magnets 16, windings 24, 25 are arranged on the free legs 19, 20 ofthe magnet yokes 16, the magnetic eld of which is formed upon applyingan electric pulse, being in an opposite direction to the field of thehold magnet at the respective print position. The windings 24, 25 are oflow inductance and the ampere turn value is regulated in such a mannerthat the magnetic iield of the holding magnet is not only neutralized orcompensated for through 4the release of bucking windings 24, 25 but isovercompensated for. Thus the crossover of the resulting magnetic lieldcomes into the range of the rapidly increasing field of the compensatingwindings, and a very lshort and exactly reproducible release or droppingtime of the print hammers is obtained. The compensating windings 24, 25are arranged by means of the insulation support sleeves 26, 27 on thelegs 19, 20 of the magnet yokes 16, without the use of the usual spools.They are connected in series and have their connections made to aninsulating plate 30 mounted on the magnet yoke through rivets 28, 29,and upon which plate they are soldered to a printed circuit 31. Thelines of the printed circuit are in turn connected to exible leads 32,33 which are secured to the insulation plate 30 by means of a clamp 34.

As already mentioned, the magnet yokes 16 are H- shaped. The legs 35, 36opposite to those on which the windings 24, 25 are disposed, serve assupports (FIG. 7). On a support bar 37 vertical bridges 38 are mountedwith regular spacing, against whose both iianks two respective magnetyokes 16 are located by means of their legs 35, 36. The magnet yoke legsare pressed against the bridges 38 by means of two tensioned and elasticU-clamps 39. A spring sleeve projecting from a hole 40 drilled throughthe support 37 serves as a stop for the tensioned clamps 39. Support 37has also holes 41 which serve for receiving a key 42, the shaft of whichhas an oval cross section (FIG. 8). By means of inserting key 42 in theholes 41, the clamps 39 can be opened by simply turning the keywhereupon the magnet yokes 16 can be released from their support.

This arrangement allows the easy and quick adjustment of the variousmagnets, which at the small tolerances normally necessary in suchprinting devices, always offers a problem of particular complexity; withthe winding 21 energized and the holding magnets 16 and armatures 15 inthe rest position, the support 37, in a manner which will be explainedhereinafter in this text, will be moved to bring the magnet yokes 16toward the magnetic armatures 15. Next, the clamps 39 are opened oneafter the other by inserting and turning the key 42, so that theindividual magnet yokes 16 are free to locate themselves independentlywith their armature 15 under the inluence of the magnetic force of theholding winding 21 without any air gaps being formed. In order to avoida shafting of the magnet yokes in a preferred direction upon the closingof the clamps, hard A1203 crystals 44 are impregnated in the contactfaces of the bridges 38, the points of which are protruding from thesurface embed themselves in the softer metal of the magnet yokes andthus prevent any sliding of the adjusted magnet yokes.

A restore bail 45 is provided to which is connected the support 37 andwhich is supported on leaf springs 49, 5l) so as to be movable to bringthe magnets 16 into juxtaposition with their respective armatures 15.Movement of the restore bail 45 and consequently also of the magnetyokes 16 is efected through a drive which in FIGS. 2-5 is shown invarious positions. The restore bail 45 has a ledge 52. In the cavityformed thereby a roller lever 53 protrudes from below. On this leverroller 55 is supported by means of axle 54, said roller engaging withthe restore bail at the contact line 56. The restore bail is in turnpressed against the roller 55 by a helical spring 57 which is supportedby a stationary machine part 58. Roller lever 53 is supported on an axle59. On its other lever arm it carries a roller 60 which engages with acam disc 62 mounted on axle 61.

For receiving the motion energy of the print hammers moving bafck aftera print impact dampers 63 are provided for the individual print hammers,the damper mass of which corresponds approximately to the mass of theprint hammer (FIG. 9). The damper material 63, Iwhich is secured toblock 65 through the layer of rubber 64, engages with the print hammersby means of locking levers 66 and consists of elastic material such as anylon composition, said levers being secured thereto at the lower edge.For that purpose the print hammers have upwardly projecting stops 67which push against the front side of the locking levers 66 duringbackward motion. For releasing the locking levers and for allowing thecontinued backward motion of the print hammers, the dampers are mountedpivoftally, the locking levers 66 being pivoted out of the path of theprint hammer. The damper block 65 is for that purpose connected to arail 7() by means of screws 68, 69, said rail being in turn secured toan arm of a pivoted lever 71. The lever 71 is mounted on axle 72 (FIGS.2-5). This axle is arranged in an offset or staggered position in adownward direction from the supporting point of locking lever 66, sothat upon upward motion of the locking lever there is little or nointerference between the print hammer and the locking lever. At theother arm of the pilvoted lever 71 a roller 73 is supported for engagingwith a cam disc 74 which is also mounted on axle 61. Roller 73 isengaged with the disc 74 by means of springs 75.

Thus the operation motion is as follows. In the rest position the leafsprings 12, 13 are not tensioned and are in a relatively flat position.The restore bail 45 is moved far enough to the front (to the right inFIGS. 2 5) that the magnet yokes 16 secured to it touch the armatures15. If the holding winding 21 on the magnet yoke 16 is energized, thearmatures 15 are held magnetically at the pole shoes of the magnetyokes. If now the shaft 61 starts its turning motion, lever 71 ispivoted by means of the cam disc 74 so that the locking lever 66 islifted upwardly out of the print hammer path. Under the influence of thecam disc 62 the restore bail 45 and support 37 are then moved back tothe left. The print hammers are carried along in the process and thesprings 12, 13 are thus tensioned. The damper mass 63 returns to itsoriginal position in the meantime. The locking levers 66 are now locatedwith a light spring tension against the sloping faces of the printhammer stops 67. If now a print hammer is released from the magnet yokes16 by one of the compensating windings 24, 25 receiving a pulse ofelectrical energy, it jerks forward, strikes the print type against thepaper sheet and is stopped in its return motion by the damper lockinglever 66. The locking lever 66 is equipped with a weight 77 so as tomake sure that upon the effecting of a print impact, the damper isalready returned to the locking position. After all of the print hammershave been released for the line to be printed, the restore bail 45 ismoved forward again by the cam disc 62, so that the released printhammers may be secured by their respective magnet yokes.

The leaf springs 12, 13 carrying the print hammers 11 are -lixed withtheir lower ends secured in the foot platen 14 as-.already mentioned.Thus each print hammer forms a structural urn't with its mounting and ifnecessary it can ne removed and exchanged fvery easily. Two associatedfoot plates 14 are connected with each other by means of screws 78, 79,and 80 as shown in FIG. l, the guide plate B1 being interposedtherebetween. The guide plate 81 is located with its stop faces 82, 83,and 84 against the block 85 and the cover plate 86, and on the otherside it is inserted in slots 87 of a plate 88. It is secured to theblock 85 by means of screw 89 and lock nut 90. The holes in the footplate 14 and the guide plate 81 for the screws 78, 79, and 80 aresufliciently large to provide :learance for the screws so that the printhammer units can be adjusted individually.

The securing of the'leaf springs 12, 13 is effected at the top as wellas at the lower end in an elastic junction (FIGS. l0, 1l). The slotsreceiving the ends of the leaf springs (slots 91, 92) are of increasedwidth in the upper portion. Besides that, they are enlarged towardstheir outer edges so as to form a cone-shaped funnel 93, 94. Therivet-shaped cavity formed in this manner is filled with an elasticsynthetic material 95 such as, for example, a nylon composition. At thetop ends of the leaf springs shoulders 96, 97 of the print hammers aresurrounded by the synthetic material 95 in order to extend the elasticjunction over the whole width of the leaf spring, which is wider thanthe width of the print hammer, the elastic material being tapered inthickness towards the midpoint of the springs. At their extreme ends 98,99, 100, and 101 the leaf springs are welded or otherwise suitablysecured to the print hammers and the foot plates, respectively.

In order to adjust for variations in the thickness of the leaf springs12, 13, spring U-bolts 102 are provided which are slidably movable alongthe leaf springs, said U-bolts fitting against the leaf springs at theirends with small rollers 103, 104 of synthetic material. The U-bolts arepositioned in grooves provided in opposite faces of, and are locked inthe foot plates 14, through the use of elastic locks 105, 106 positionedin the grooves 107, 108 and fitting against the bolts under pressure.These slidable U-bolts have the function of adjusting the action of thesprings 12, 13 to compensate for minor manufacturing tolerances in thethickness of the leaf springs, and permit a relatively fine adjustmentof the hammer flight time.

Referring to the FIG. 12a, it will be seen that the holding winding 21which is common to all of the magnetic yokes 16 is connected to thepositive terminal of a 38 V. source and to ground, through an inductancedevice L and a series resistor R. The bucking or neutralizing windings24 and 25 of the individual magnet yokes 16 are also connected to thesame source through a resistor R1. The series resistor R1 is bridged bya capacitor C1 in order to effect a quick rise time of the magnetizingcurrent. Again it is emphasized that the holding winding 21 is common toall of the magnet yokes 16 whereas the bucking windings 24 and 25 areindividually arranged on each yoke and can be controlled individually.

For that purpose, the other end of the series connected windings 24 and25 is connected to the collector of a transistor TR1 whose emitter isconnected to ground or zero potential. Normally the transistor TR1 isturned off, but if a pulse is applied to its base by way of the ANDswitch A1 this transistor is turned on, and the bucking windings 24, 25are excited for a relatively short time.

The transistors TR for each of the print positions are controlled asfollows. The memory storage of the machine contains the text of a printline. By comparison with an electronic image 0r representation of thecharacter on the type bar it is determined after each step of the typebar how many further steps of the type bar are required each time inorder to make sure that a type character corresponding to the characterto be printed in a particular position is located opposite this printingposition. If the number of steps required equals zero, that is, if acharacter to be printed lies Opposite the particular printing positionin question, the corresponding AND switch A1 is prepared by raising theline x. When this has been carried out for all of the printing positionsfor a particular position of the type bar, a pulse is applied to raisethe line y of all AND switches A. Thus the transistors TR1 are turned onand the corresponding windings 24, 25 are energized, so that the printhammers are released, and a print impact is obtained in all of thoseprinting positions lwhere the AND switches A have been prepared byraising the line x. By having the bucking windings 24 and 25 producing asufficiently strong magnetic field, the magnetic eld of the holdingwinding 21 is more than neutralized, and is overcompensated, therebyforcing collapse of the holding magnet field more rapidly and areduction of the hammer flight time and a stabilization of the system isobtained.

In FIG. 12b the hammer flight time dependency on the ratio of the ampereturns of the bucking windings and of the holding winding, is shown. Thisshows clearly that the hammer flight time decreases with increasingvalues of a, and that between the values 1.6 and 2.0` it passes througha very flat minimum and that it subsequently rises again. The mostfavorable value of a is at approximately 1.76; considerable variationsin the values can occur, however, without there being any exceptionalchange in the hammer flight time, because of the flatness of the curvein this area.

The low influence of voltage variations can be seen by referring to FIG.12c where the hammer flight time is plotted against relative variationsin the potential of the 38 v. source. In both FIGS. 12b and 12o thenormal variations are indicated by the hatched areas.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a print hammer unit for a high speed printer 9 having movablemeans for presenting a plurality of type characters at a print line forcooperative print Uaction by print hammer means,

a print hammer having a hammer portion adjacent the print line at eachof a plurality of print positions and having an armature portion,

resilient supportmeans for each of `said hammers including a pair ofparallel flat spring4 members, .Y

means including electromagnetic means having a separate magnetic yokeatVV each print position with a single hold Winding common to all of theyokes operable to produce magneticfiux in said armature portions to holdsaid armature portions away from the print line and flex said springmembers to store potential energy'therein, v means operable to effectmovement of said hammers in response to said storedy energy by'reducingthe flux in the armature portions below the holding point to effectrelease of said hammers. v

2. In a print hammer lunit, the combination in accordance with claim 1,characterized inthat for the deactivation of the electromagnets holdingthe tensioned print hammers, individual release windings are arranged atthe various print positions on the magnet yokes in such a manner thatthe magnetic field produced by them neutralizes the holding magnet fieldand removesit from the armature, respectively. I 3. In a print hammerunit, the combination` in accordance with claim 2, characterized in thatthe magnetic iield of the holding magnet is neutralized through themagnetic field of the releasing magnet individual to the correspondingprint position. f j

4. In a print hammer unit, the combination in accordance with claim 3,characterized in'- that the holding coil which is common to all magnetyokes'and continuously carrying current is connected to a source ofelectrical energy in series with an inductance device of a high value.

5. In a print hammer unit, the combination'in accordance with claim 4,characterized in that the magnet yokes near the pole faces have a crosssection which is 'reduced compared with the remaining magnetic circuit,and that in this area they are magnetized to the saturation point.

li. In a print hammer unit, the combination in accordance with claim 5,characterized in that-the magnet yokes, preferably in pairs, are fixedon bridges mounted on a common carrier by means of tensioned clamps.

7. In a print hammer unit, the ,combination -in accordance with claim 6,Ycharacterized in that the surfaces of the bridges, and the inside jawsof the tensioned clamps pressing the magnet yokes against thebridges,-are impregnated with hard crystals, preferably sintered A1203(corundum).

8. In a print hammer unit, the combination in accordance with claim 7,characterized in that the magnet yokes are aligned individually towardstheir print hammers in such a manner that they automatically locatethemselves when the holding magnet is excited and clamps opened by meansof a key, and under the influence of the magnetic forces the tensionedclamps are held against the corresponding armature without an air gapbeing formed.

9. In a print hammer unit, the combination in accordance with claim 8,characterized in that carrier of the magnet yokes is supported on leafsprings and arranged in shiftable manner, and that cam means is providedt actuate the carrier and provide a motion which goes back and forthperiodically and which is also directed perpendicular to the platen,said motion serving for the restoring of the red print hammers.

10. In a print hammer unit, the combination in accordance with claim 9,characterized in that the print hammer units; preferably in pairs, arefixed in such a manner that they can be adjusted individually, as theyare secured to their foot plates by stationary guide plates.

11. In a print hammer unit, the combination in accordance with claim 10,characterized in that the leaf 10 springs carrying the print hammers aresurrounded at their top and lower ends with coatings of elastic materialwhich fill cavities recessed in the print hammers and the foot plates,said cavities having the spring ends welded to their innermost ends, andthat these coatings taper continuously towards the middle of the spring.

12. In a print hammer unit, the combination in accordance with claim 11,characterized in that spring U-bolts are provided which are shiftablealong the leaf spring pairs carrying the print hammers, which furtherfit with their end points against the leaf springs intermediate the endsthereof, and which are combined structurally through being slidablysupported yin the foot plate of the corresponding print hammer unit, sothat these bolts serve for the adjustment of the hammer fiight time.

13. In a print hammer unit, the combination in accordance with claim 12,characterized in that at the individual print positions elastically xeddamper masses are provided which absorb the energy of the print hammersmoving back after print impact, and which, by means of elastic locksblock the print hammers until the magnet yokes are' moved to their frontextreme positions to seize the print hammers.

14. In a print hammer unit, the combination in accordance with claim 13,characterized in that the damper masses are fixed on a common carrierextending over all print positions, pivotally supported with its pivotpoint positioned below the elastic locks, said carrier being pivoted formovement for a short time for releasing the print hammers, preferably bymeans of a cam gear.

l5. In a fiexure spring mounting arrangement wherein at least oneJlexure spring means is joined to a relatively rigid member at a bondingsurface thereof so as to be bent flexingly with respect thereto, animproved com-posite joining arrangement comprising:

cavity means for each spring means extending into said surface of saidmember; metallic bonding means lixedly connecting one end of each saidspring means to said member, at the inner portion of said cavity means;and elastomeric fillet means adhered Abetween each said spring means andsaid memlber along a portion of said spring means adjacent saidconnection with said bonding means so as to graduate the stiffnessgradient and damp out extreme stresses therealong.

16. The combination as recited in claim 15 wherein said bonding means isadapted to fuse with said member and each said spring means for a rigidbona' in the innermost portion of said respective cavity means; whereinsaid fillet means fills the balance of each said cavity means; andwherein each said spring means comprises a fiat strip flexure.

17. The combination as recited in claim 15 wherein said member iscomprised of a rigid metal; wherein said bond connection comprises awelding between said flexure spring means and said metal member andwherein said elastomeric fillet means encapsulates and adheres theassociated end of each said spring means, coupling it dampingly to saidmember.

18. In a hammer assembly including a rigid base member, a slug memberand a pair of flexure strips mounting said slug member from said basemember so as to be pivoted relative thereto at high speeds and underprecise guided alignment over an extended operational life, theimprovement in combination therewith of a composite bond arrangementbetween the base end of each said flexure strip and` said base member,said bond arrangement comprising:

a pair of cavities provided in said member so as to include innerenlarged portions; rigid metal join means rigidly connecting the baseends of each 0f said jlexure strips to said member at a respective oneof said enlarged cavity portions; and graduated damping means couplingeach said fiexure strips to 1 l said base member resiliently, adjacentsaid respective rigid metal connection, thereby occupying outer portionsof said cavities.

19. A method for bonding a flexible spring member to a relatively rigidbase member with improved maintenance of a fixed orientationtherebetween as well as improved and extended operational life, nospring breakage and the like, said method comprising.'

providing a cavity in said base member;

rigidly bonding one end of said spring member to said base member at theinner portion of said cavity by fusing material therebetween; and

coupling a graduated-flexibility damping means between said memlbers,along a portion of said spring member adjacent said fusion bond.

20. The combination as recited in claim 19 wherein said rigid basemember comprises a metal base fram-e; wherein said spring membercomprises fiexure strips; wherein said rigid bond is provided by weldingthe base ends of said flexure strips each to an associated portion 2()of said fram-e; wherein said damping means is provided by flowing anelastomeric potting compound about portions of said frame and about saidspring members, at least adjacent said weids, and curing it both toencapsuf 12 late said frame portions and to provide said stress dampingadjacent said welds.

References Cited The following references, cited by the Examiner, are ofrecord in the patented le of this patent or the original patent.

UNITED STATES PATENTS 2,940,385 6/1960 House 101--93 3,041,964 7/1962Simpson et al 101-93 y3,144,821 8/1964 Drejza 101-93 3,145,650 8/1964Wright 101-93 3,156,180 11/1964 Barnes 101-93 3,172,352 3/1965 YHelms101-93 3,188,946 6/1965 Schacht 101-93 3,209,682 10/1965 Cooper 101-933,266,418 y 8/1966 Russo 101--93 3,289,575 12/1966 Wasserman 101-933,049,990 8/1962 Brown et al. 101-93 WLLIAM B. PENN, Primary ExaminerU.S. C1. XR. L29-428

